1. Field of the Invention
The present invention relates to an image forming apparatus such as a color copier, etc. equipped with a device to make the judgement as to whether input images are specific documents such as banknotes, securities, etc. and an image forming method.
2. Description of the Related Art
In a conventional color multi-functional image forming machine, when the copying is made, a document was placed and fixed on a document table and a document image was read by moving a scanner (hereinafter, this operation is described as a fixed document reading). Further, in a color multi-functional image forming machine, a means to detect a specific document and a means to smear away the whole surface of the image data when a specific document is detected by this detecting means in order to prohibit the copying of the specific document.
In recent years, with the speed-up of the color copying process, a system with an automatic document feeder (hereinafter, described as an ADF) installed to a color multi-functional image forming machine to read document images by a reading device while moving the document is increasing used.
In the Japanese Patent Application Publication No. 8-37595, a technology to make the judgement as to whether input images are specific documents such as banknotes, securities in a color copier using an ADF equipped with a specific image discriminator is disclosed.
However, a system equipped with an ADF to read images of documents, which are being moved, is susceptible to color shift by vibrations or other factors when compared with a conventional system to read fixed documents using a scanner that is moving. Accordingly, there is such a fear that a recognition rate of a specific document sensor retained by a color multi-functional image forming machine may drop depending upon kinds of specific documents such as banknotes, securities, etc.
On the other hand, a reading magnification (a reading speed) of a color multi-functional image forming machine equipped with such an ADF is normally adjusted for a simple body of scanner or a simple body of ADF at the time when an apparatus is assembled or installed so that the set copying magnification comes to agree with a copied image output from a printer. Definitely, when a document is read actually using an ADF and a scanner and the copied image is output by the printer, the magnifications of the scanner and the ADF are finely adjusted, respectively and the magnification of the copied image is adjusted properly. For example, when a magnification being set with a control panel is 100%, the scanner magnification is set to 99%, or the ADF magnification is set to 98% so that the image outputted by the printer may become 100%.
Furthermore, since the reading magnification read by the scanner or ADF was different as described above when the magnification inputted from the control panel is set as a specific document detection unit, there was a problem that a recognition rate further falls.